Journal
CHEMISTRY-A EUROPEAN JOURNAL
Volume 11, Issue 5, Pages 1495-1506Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/chem.200400867
Keywords
aggregation; diffusion; lithium; NMR spectroscopy; X-ray diffraction
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Li-7, P-31, and H-1 variable-temperature pulsed gradient spin-echo (PGSE) diffusion methods have been used to study ion pairing and aggregation states for a range of lithium salts such as lithium halides, lithium carbanions, and a lithium amide in THF solutions. For trityllithium (2) and fluorenyllithium, (9), it is shown that ion pairing is favored at 299 K but the ions are well separated at 155 K. For 2-lithio-1,3-dithiane (13) and lithium hexamethyldisilazane (LiHMDS 16), low-temperature data show that the ions remain together. For the dithio anion 13, a mononuclear species has been established, whereas for the lithium amide 16, the PGSE results allow two different aggregation states to be readily recognized. For the lithium halides LiX (X = Br, Cl, I) in THF, the Li-7 PGSE data show that all three salts can be described as well-separated ions at ambient temperature. The solid state structure of trityllithium (2) is described and reveals a solvent-separated ion pair formed by a [Li(thf)(4)](+) ion and a bare triphenylmethide anion.
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